The switching power supply circuit does not vibrate
To repair the switching power supply that does not vibrate, you can take the optocoupler as the demarcation point, first determine whether the fault is before the optocoupler or after the optocoupler, and then narrow down the scope of investigation step by step. The specific operations are as follows: first short-circuit the optocoupler directly, then It's very simple, just solder it with a lump of tin, which is equivalent to reducing the internal resistance of the optocoupler. After the optocoupler is short-circuited, we measure the voltage again. If the measured main voltage does not change, the fault is in the circuit behind the optocoupler, and vice versa. , before the optocoupler circuit. Here the switching power supply should carry a light load, and some switching power supplies will not vibrate without a load.
If the fault is in front of the optocoupler, mainly check whether there is a problem with the AC input, whether there is an open circuit in the capacitor circuit, and whether there is a management chip to check whether the power supply of the chip and the ground voltage of each pin of the chip are correct. Although we short-circuit the optocoupler, we also need to rule out whether the optocoupler itself is faulty.
If after the optocoupler, check whether the switching transformer has inter-turn short circuit or open circuit, if it is found that the switching transformer has a short circuit, then it is necessary to suspect whether it is caused by the short circuit of the peak absorbing circuit to prevent misjudgment, because the probability of the switching transformer being damaged Very small, shorted PWM transistors can also cause the circuit not to oscillate.
If you have insufficient maintenance experience and cannot determine whether the original is damaged online, it will be more troublesome to take it down and measure it, which is more accurate. If there is no problem with the removed original parts, then you can check the relevant small devices associated with the fault, gradually narrow the scope of the investigation, and determine the problem. If you scratch the beard and eyebrows together, it will easily lead to a loss in the face of the fault, and you don’t know where to start.
As for the so-called start-up, I will also give a simple explanation here: in the process of changing AC to DC, the AC mains is firstly rectified and filtered to become DC, which is used for the electronic circuit to work. This circuit includes a high-frequency oscillation circuit. That is to change the DC into a pulse with variable frequency or pulse width. This part is very important in the switching circuit. When the input voltage changes or the load increases and becomes smaller, the oscillation circuit will keep the output stable by adjusting the frequency or pulse width. This is Its role, in order to play this role, of course it must start to vibrate. If it does not vibrate, it means that the switching power supply is out of order, which is equivalent to over-adjustment or no adjustment.
